Does a car speedometer me* dly+ wy3));n2plxqiro by*c asure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If y :w 4*w3ik+y)pblm3 jw6hgcp yes, give examc4h3j3 bi w6 gwkp*lw+ yy)pm:ples.

When an object moves with constan kr1.8 zpmt kq9:krtnq/ mzh4,t velocity, does its average velocity during any time interval differ froz p1 q.n:m,r48t/kzmkt 9hrqk m its instantaneous velocity at any instant?

In drag racing, is it possible for the car witpml6ml 5 vy(o(h the greatest speed crossing the finish line((m6lom5py v l to lose the race? Explain.

If one object has a greater speed than a second object,ir5qjg22b+ )m) qzmgaovg3v7 does the first necessarily have a greater acceleration? Explao3rgi m5v+ a)qg2 qzbjmv72g)in, using examples.

Compare the acceleration of a motorcycle that accelery is:9+y; ux:xxo c/ dk-jwe9cates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10ky 9:d /x:ix9eusx +;cy-owjc km/h in the same time.

Can an object have a northward velocity and a southward acceleration? Eko2ni:p 9. yly8;aajjxplain.

Can the velocity of an object be negative when its acceleration isp:lvhfr s8x pp h,x/bu-39d5 i positive? What about vi3,/fulid-phs xx8p: b 9 5hrpvce versa?

Give an example where both the velocity and acceleration are negativo ez0,6e6pt jme.

Two cars emerge side by side from a tunnel. e/;v(kz,ol f*thndnqxg1l;.Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is pass,el1.nngf;h(x vt*;/ d lkzqoing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in sphtf5:e, s3a ypb)njnmw/4 efn8beg4s b2q+x/eed as its acceleration decreases? If so, give an example. If nop4hnswgbnff2 / )4te+8my3/j bsex q5na,be: t, explain.

A baseball player hits a foul ball m u k2vbn;)14v2dvw9te d5kvu straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?ve92;1 mk tvb uv2d54nwd )vuk

As a freely falling object speeds up, what 4/q2/q uuqnh ,7bcflvis happening to its acceleration due to gravity — does it increase, decqqv,f/bclquun2 h7 /4rease, or stay the same?

How would you estimate the maximum height you could throw y1adx*u6em ds;79lcoo xy9i9 a ball vertically upwar9xcl; o1em9*s9y76 yu xoadidd? How would you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a co883: )e*soxzbf.pz 7qyg k kaknstant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why k z )8fep7b.*gq kox:kays8z3 or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts ti cbn7g3lfv-1zqd+ a x(ed to it at equal intervals is dropped from the ceiling of the lecture hqxa dc73(b vf+ nl-gz1all. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motion9 utu+r)jfd ); fk)dggs is not at constant acceleration: a rock falling from a cliff, an elevator m dg))j9tr+g; d)fkfu uoving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thro4,x1bbfj:9es:e3d g wo6bzl ze )f*knwn vertically upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if sog6w z,xj kn1ld4bb9):* sf: ebze3eof, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same time? G9w .3x*oiu u drvlq2w1ive examplxl*9o.w 1 r3d2q uivuwes.

Can an object have zero acceleration and nonasows hpvq)l +b46)2g zero velocity at the same time? Give examvsq6p+4b hw2sa o)l) gples.

Describe in words the motion plotted in Flq 07 siupxg*1ig. 2–28 in terms of v, a, etc. [Hint: i0xu1psq* lg7First try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motrig r+ zuh4+z )+/vg-kolv j6pion of the object graphed in Fig. 2–29.

  What must be your car’s average speedd1qg7xcwy9k6lh e87g,.h znq in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/rt s4si12 (kep.ea4cth How long does it take to fly 15 km?    h

  If you are driving along a strai zgmeta b-:b)bb1dg 30qin52lq-l4f nght road and you look to the side for 2.0 s, how far do you travebgadtl: 1q lmb02 4q5z feg)bnin-3- bl during this inattentive period?    m

  Convert 35 mi/h to tc7afs+r/r-9 fo0u0w nt0tcg
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fro3o3 ufp k5fw,x d6xdg3m $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home fr 9e;9ifkfmak 9om school steadily at 95 km/h for 130 km. It then begins to rain and you slow tm9efki9 a9 f;ko 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightning flash and ts 7iw hf;2ds85b5mbfehe following thunder gives the distanceiw 8f5 7h;5e2sfbd bms to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a totackrr (/5mjf. ao.c r 1/xj2ruzl time of 12.5 min. Calculate5kcx(rja/ro/. jfm u rzc. 1r2
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away f5ud)coqdd- t:h.n 6tzrom its trainer in a straight line, moving 116 m away in 14.0 s. It theh)d:tc qod5tz d.u-n 6n turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracs(- qg 7rnxg;cot3n 9bks. Each has a speed of 95 km/h with respect tcg 9-o37;brq snxg(tno the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 kmir84v7f/gcvd., u;fe w4 wqv s,k vhx)/h is 110 m behind a truck traveling How long will it take the car to reach the tru k,qffvvivdvw;we h.rxg s/ 8c4 74,)uck?    s

  An airplane travels 3g)*;vo xy.8) x *o3w8fri/oz )siqg,qntj fhh100 km at a speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next hnxr/,ij v h)8t8)3oo )fxg *gq*fy.; sqwozi2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of akxxht x;jr+f5g/x52w j*c az1 complete round-trip in which;a2 +zwg ct*rfx5xx 1 /xj5kjh the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at theuap91 d59byohrw(.wt. ua sx- end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 ups9w.uda9xr 5.w-oyab th 1(s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. Wh zxvi /043.p ys3:t2ycaqcid wwfh:u jg1(t0fat is its average accelx dwy3(c0h j2: 31.y04zuc:ivsifgwp / taqft eration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates r, p7/jhvid0 rfrom rest to 10.0 m/s in 1.35 s. What is her acceleration d p,7rh0rvij/
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobif ijm/ ue.qgp jvf vg8co3np(v7 /63+xle is capable of an acceleration of aboutcjqj83pum6 o v(/3i g ef7xp+ng/fv.v $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110 m in 5ugq3vnwkgqz.22 ar8 ;.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accele; a gr2z3uk8n.2vqqw gration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts fr-2rc- vnmerw(az yu( )6o,awu om rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estr2(6r w-nm-v,z)u (cuaw oyeaimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What;wgzanu:i*n595 ik ub was its acceleration? How far did it travel in this time? Assume constant accelerati5*ui 9 n;wgi5buazk n:on.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was ;1a2c)s edesbm :e5phits acceleration, assumed conm pess1e5:) ;ah2db cestant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long*eo1v2uf tjlzs( aj82 a runway is needed if the (consv*zto8aslf 1uj2( 2e jtant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocksqr idhnx f82-az,b9 .f to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this d-aih b nrfq8.2,9zx fsprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of hm6* xhul2ad9a:l m(p kd(q)u 12.0 m/s to rest in 6.00 s. How far did it travel in t6h9*l(qmadm )kuxh 2ul(d :pahat time?    m

  In coming to a stop, a car leaves skid marks 92m0;nuks f( ajsky9gqxp va,56s8mz92 m long on the highway. Assuming a deceleration of8j2u9 s,; a6s05pamkk n gsz(9m yqvxf $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes :,cftxq(/ .bfd *l vnna tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.0flbvn xqc/f:. *d t,n(0 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distansddx)oiu3wxa /)p 3)tces for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an accuaxd 3d3x)) w/ )pitsoeleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping dista /0mwg*y jqxh snc5m:9nce of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver looks -8e:bdt a6crn for an opportunity to pass,tebd68a -r :cn guessing that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,002g +lxt hb87gg0-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The x2hgtb g7g8l+runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches u*: z(epjl4 ujan intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s 4ljpje *zu(u:before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground pql6gjiy s8.ye xo-l 2h* zh-5below after 3.25 s. H6 gyyjhl.s- -eozlp8x5h2*iq ow high is the cliff?    m

  If a car rolls gentlye6vul )bz(((jipi(g c ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up i*4vgzm,uu 3gunto the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it nip )gx-sa-t( dqn;-aj k-avp12m9s6p hndu6vertically upward. With whatasd6ns(ppp-uk n-aij gnxd v1- - t m2)9aqh;6 speed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Drawm eux 7tb3;ys) graphs of (a) its speed and e u)bysm 7x3;t(b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height l yz:d58yzc*y v /lt1cof 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicoptyy* c:dvzltl/y1c8 5z er’s.] t =__ s

For an object falling freely from rest, show that the distance traveled dur80bgbf)7wh2lof*3 l7 t* 2j, wiisvsixb8xiking each lisxb8i*v3fs 7gw2k7i i 8l0hf 2wxotb*jb,)successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algeb)lh:lmjy ,s 9:- p)pofygzu w9raically) that a ball thrown vertically upward :yppm-w y)j)9u l,9 zoflg:hs with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upwa9o6 tcuq.2r nmrd with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the app9n ojlvgyc:o;5ve*bb6i9 :/f k ht1,o y adi1sle in Fig. 2–18 (or number of phjbdhk* oa9 of;i6silv:51g:y ,tn/9 cb1evy ootoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.2z 6atkzm3o8/w. ibn+h4fus8 j 8 s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window didfb.4a/uz8 mihs8n+ k3otw6z j the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking yei a/gg 4/jg9beu30t the ocean is heard 3.2 s later. If the speed u e9beg4a3 0t/gyji/ gof sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard streaf(gg2txx,wl 8ve, xxecnia z*3 )78yz m of water. You point the nozzle vertically upwardv ex xxf gz,* w8n8lg2iac,tz y3(xe7) at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of a k(h v:9 p,yfln1fh8tkcliff 70.0 m high (Fig. 2–34).hl p1tvyh8 9fk(f:,nk
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a windowylo 0ck5 6ftmv0 1gua+n.0t ou 28 m above the street with a vertical speed of 13 m/s If the ballt6.an kovu 0y+u om150c lft0g was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the ve,7z,vub vu+thxa4 h.jlocity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what pev u7tujb hzxh.+,a,4v riods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of tp wpuk4a0x41 qime is plotted in Fig. 2–28. What ip ak44 wqupx01s its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accelerate approximately as s )7 w3yvrps54vzdxq*o e/nr7uhown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gea5 *e)onry/d7 wps73q4rv zu vxrs.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average accelera mwt ec0gx80,jtion of the car in the previous Problem (Fig. 2–35) when 00xgcwmjt8e, it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the objek w 5yjqeqpaboab3 u n-2a,vm;tn+a)(w)/7 ofct traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a functzq;)g uh5kiuzy . 5o7p: a+oroion of time is giuq +k5ugy 5haooo. 7r)z:z;p iven by Fig. 2–28.

Figure 2–36 is a position verp9*+ gyjed ,fnosu9o( sus time graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object po9s,o9d *pgfjo + (uenysitive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m abovm7evp frec,k +(o2j, smo 1i)se a firefighter’s safety net. The jsc p+7mkm ,o 1,i2(reove)sfsurvivor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on Eke- d .;yd9uo1zk m(ajarth. If an object is thrown vertically upward on the Moon, how many times a1m;jydd keu (k .o9-zhigher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properlycq+5t:g:zav-;hlx,r+c6hb ; *wteh mr nmwe/ constrained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the dehc;,zmx m tc hl r +- e;agh:w/bq5tn+w*6:evrceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his pursuersf.s /6: r(m:anpdxfh erkdt l*-ua5(u are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates h.rk a*dud ns p-frext/u(:5(l :afm6 how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its z mafz(8)eq17 h4nqv,q mek-acars for front-end collisions by hauling them up on a crane and dropping them from a certak8qzqq74 ) mmf- eazh1e v(a,nin height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels absx3s/-ntz3( 2dew wgyout $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of the t2g6 jvybt d8l)rain has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the d2 l)y8tv6 gjbtrain started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.*t.z 4rsxcma7 0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under mt7azx.cr* 4s the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the ave 5we5xy4 s b+)koei)j qg2+lmbrage speed of a train against the distance between stops. The more stops there are, thekebg q)sjmoyb 2xw )e +il554+ slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings u9i1hbtyl.u23y p/ebnk aj4j1n c; wlk /j0d*and free fall straight down when diving for fish. Suppose a pelican starts its dive from a height ot/u ukl*4.b0;k/cd jjy jynl w9 phe312a1ibnf 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planned so t6: z9-mnix xgfhat the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on axm9 :-inf6 gzx particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at 7*rib z18pjepa constant speed of 6.0 m/s Just as an empty box car passes hjp e8r1bz7*pi im, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a hig cvq b/j24 /lclbg56il,nuq,sv9c5vs h building. A second stone is dropped 1.50 s later. How far apart are the stones when the sei jg/4 cv/ q,qcn6 v5sbbv,c5usl92llcond one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the courodn 6 arw-j7 y9csv)fj*7co3 g ,4eccjse of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?-nrg7 jo*s 9 j a4fccj,e o6)wydcvc37    km/h

  A bicyclist in the Tour de France crests a mountain pass as he movo)rmt/u iba :(c(vl n4es at 18 km/h . At the bma b /i:nl)4tocr( (vuottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounce up one-a::pps 4oqu vj5 cizki4y6e. ;xnd-a-half times higher than the second chii z 4q;s vp5pj4ci:x6yu.:eokld. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long trainhgzh( r)iwy ho v*d-y4/ 3s(sr44y oeu traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how) /h yh4v ioy4(*rg4(z3u sds -rwheyo long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 6ngd s;8u6jw x((cywjs *- rirm/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 mwwjrj6s(nx s 68 gui;dry(c*-, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerm: vo2l, a jr5t:vj+vxation of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–2 e ewnhm*z39y42. Each intersection has a traffic signal, and the speed limit is 50 km/3eyeh29nm *zw s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveli-cq o1z)cscg3bb(( czng at a constant 120 km/h takes off in hot pursuit. The police offics )gc (1-bozbcc(cz3qer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 1naktq gpa6 82jpf9e(2.00 s after that, a second stone is thrown straight down with an initial spepg6nft9akp2( e18 a qjed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown verticallm: lbc2dzkliy0f/ x5w)ro3 s*y up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thr3w) o/xlk2iy*0dml5 cs zfr:bown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long p d3 sdrqj(2)nwould it take a free-falling parachutist to fall from a plane at 3200 m to an altitude ofjrq d)(3s np2d 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers throubfw58d l isl/4gh a grilling machine. If the grilling machine is 1.1 m long and lf4swld 5/8ibthe burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than lx;16sq xyd*f7imwx8 Joe can. How masx;q18*d7x 6 my xiwlfny times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stawbs-vf 5b/oe,5 *hw-n2khoxy nds on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, suny skf -*wbobhve/2oxh5 ,5w-ch that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particmwvqto e:w )2mfeij27,bb *s/ular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s ej,ows qmwf 2)/2:tmebvi*b7 make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for /uzrmaq/k:9t two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higq9k r//ua m:zther average velocity?